This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Pre-imaging measurement of the transverse relaxation constant, T2, in samples intended for examination by pulse ESR Microscopy (ESRM) is important for understanding the Gz gradient requirement for slice resolution, the Lorentzian lineshape, and effects such as oxygen concentration, viscosity and relaxation times. An important advantage of pulse ESRM, the ability to acquire several types of image contrasts, also requires a priori knowledge of the sample's T2 parameter. For our current principal ESRM operating mode, a relatively simple two pulse spin-echo sequence is employed that avoids the need for short, precise rectangular Gz pulsed gradients and rectangular Gx and Gy gradients. For this pulse sequence, it is advantageous to know the sample T2 as the optimal pulse spacing is directly related to it. By means of an extension to the existing ESRM VI (LabView virtual instrument) application that we have recently devised, direct measurement of T2 can now be made prior to imaging studies when prospective samples have been inserted into the ESRM probe resonator. Only the pulse sequence differs between the two measurement modes, with no gradient pulsing occurring during the T2 measurement. In the ESRM imaging sequence, the Gx and Gy pulse gradients are stepped sequentially through their respective intensity ranges with the pulse sequence timing and pulse widths remaining constant. For the T2 measurement, the [unreadable]/2 and [unreadable] pulses remain fixed in width but the interpulse spacing is sequentially stepped out. At each pulse spacing step, the echo signal is recorded (typically with a small z-gradient applied to somewhat broaden the echo signal). When the complete data set has been collected, the amplitudes of the echo signals are extracted and plotted against the pulse spacing time and the plot is exponentially fitted to derive the value of the T2 transverse relaxation time parameter.